1. Field of the Invention
The present invention relates to a camera device for imaging a plurality of directions in the visual field simultaneously and a vehicle periphery monitoring apparatus using the camera device.
2. Description of the Related Art
There is proposed a camera device capable of imaging a plurality of directions in the visual field simultaneously as shown in FIG. 8.
A camera device 100 includes an image pickup unit 101 having a single image pickup device 110 and an image pickup lens 112 disposed in front of the image pickup device 110.
A prism 120 is disposed in front of the image pickup unit 101 on the upper side. Incident beams entering from both of the left and the right sides are guided by the prism 120 toward the image pickup unit 101 so that an image is formed on the image pickup device 110 via the image pickup lens 112.
A wide-angle lens 122 is disposed in front of the image pickup unit 101 on the lower side. An incident beam from the lower side is guided by the wide-angle lens 122 toward the image pickup unit 101, so that an image is formed on the image pickup device via the image pickup lens 112.
In other words, it is structured in such a manner that images of the visual field in both of the left and the right directions in front of the camera device 100 in the upper region Vu of the vertical angle of view of the image pickup unit 101 are picked up with the intermediary of the prism 120, and an image of a visual field on the lower side of the camera device 100 in the lower region Vd of the vertical angle of view of the image pickup unit 101 is picked up via a wide-angle lens 122.
A predetermined image processing is performed for an image picked up by such camera device 100 and the image after processing is displayed on a display device, such as a liquid crystal display device.
An example of the image displayed on the display device will be shown in FIG. 9. In FIG. 9, images of the visual fields 142L and 142R on the left and the right sides in front of the camera device 100 are shown in an upper half region 141 of a display image 140, and an image of the visual field 144 on the lower side in front of the camera device 100 is shown in a lower half region 143 of the display image 140.
As a publication disclosing a camera device capable of imaging a plurality of visual fields simultaneously, such as the one described above, there is a document JP-A-2000-089301, for example.
However, in the camera device 100 shown in FIG. 8, there is a problem in that the ineffective region VR, where an image cannot be picked up, is generated between the upper region Vu and the lower region Vd, and a relatively large ineffective region 146 is generated between the images of the visual fields 142L and 142R on the left and the right front sides and the visual field on the lower front side 144.
The reason why the lower ineffective region VRd of the ineffective region VR is generated is as follows. In the camera device 100, a supporting member 130 for supporting the prism 120 from below for supporting the same at a predetermined position is disposed on the bottom of the prism 120, that is, interposed between the prism 120 and the wide-angle lens 122. Especially when the construction in which the prism 120 is inserted into the camera device 100 from above is employed, provision of the supporting member 130 on the bottom side of the prism 120 is substantially required. In such a case, the supporting member 130 is disposed at a position relatively close to the image pickup unit 101, and thus the supporting member 130 is to be imaged over a relatively large angle of view.
The upper ineffective region VRu is generated by the difference in index of refraction between air and the prism 120. In other words, when a light beam enters into the prism 120, the light beam is refracted to a direction closer to the normal line of the incident surface of the prism 120 by the difference in refractive index between air and the prism 120. Therefore, the light beam entered into the prism 120 through the bottom of the prism 120 is reflected irregularly from or absorbed in a rough surface of the bottom of the prism 120, and thus will never form an image on the image pickup device 110. In this manner, the upper ineffective area VRu is generated due to the difference in refractive index between air and the prism 120.